The present invention relates to a semiconductor integrated circuit device such as semiconductor integrated circuit device, especially relates to a semiconductor integrated circuit device on which are mounted elements or circuits possibly to overheat and on which is mounted also an overheat detection circuit.
As an overheat detection circuit mounted on the integrated circuit, those circuits shown in the drawing FIG. 4A through FIG. 4C have been known. In FIG. 4A, the circuit utilizes a thermal characteristic of diode""s forward voltage drop, which detects the temperature of a place where the diode is located, and the said circuit produces an overheat detective signal when the temperature reaches a certain degree.
In FIG. 4B, an output is produced by the overheat detective signal in accordance with the increase of the leakage current of the base opened transistor, i.e. the increase of the backward current of the parasite diode between the base and the emitter indicated by dotted line.
Furthermore, in FIG. 4C, the overheat detection circuit senses the temperature by using the thermal characteristic of the constant-current source 1 and bipolar transistor 3 through the base resistance 2, and at the same time amplifies the detection current.
For that reason, this circuit is designed to flow the output current of the constant-current source 1 from the joint of the base 3 of the transistor 3 and the base resistance 2 to the base resistance 2.
And the collector current of the bipolar transistor 3 is transformed into the voltage signal by the pull-up resistance 4 and this voltage signal goes through the buffer 5. Thus the overheat detection current might be produced. The base resistor 2 is usually formed by a semiconductor pattern and so forth, surrounded by the well region 2a which is clamped to the base 3a of the transistor 3 in order to be isolated from the other circuit elements.
However, the above-said known overheat detection circuits used for the semiconductor device has advantages and disadvantages at the same time. For example, both the circuit shown in FIG. 4A and the circuit shown in FIG. 4C have an advantage and a disadvantage. It is easy to define the temperature freely to produce the detective signal, but it is difficult to match the transition into the overheat condition to what temperature of the detection.
As to the circuit in FIG. 4B, an advantage, on one hand, to detect correctly the transition into the overheat conditions since the leakage current changes rapidly in accordance with the overheat conditions. On the other hand, it is difficult to design a circuit to obtain the stable operation.
As the circuit in FIG. 4C has a base resistance, it is practical to use the circuit and it has an advantage to utilize the current amplification of the transistor without further additional elements.
In considering the above-said problem, such an overheat detection circuit is requested as can detect correctly the transition into the overheat condition and is easy to utilize. In replying to the request, one idea is to make react to the leakage current as in FIG. 4B, maintaining the advantage of the overheat detection circuit as in FIG. 4C. Therefore, it is the technical problem to improve the detection circuit based on the circuit in FIG. 4C.
It is an object of the invention to realize the semiconductor integrated circuit device which detects the overheat by way of the leakage current of the base resistance of the transistor The above mentioned object of the present is accomplished by using the leakage current of the base resistance of the bipolar transistor. It is an object of our invention to realize a semiconductor integrated circuit device which detects an overheat condition of the elements protected from an overheat is realized. That is, the overheat detection circuit is formed on the same substrate where the elements or the circuits which are protected from overheat are formed. The said overheat detection circuit comprises a bipolar transistor, its base resistance, and a constant-voltage source. The said constant-voltage source provides a certain voltage necessary to isolate the elements. In comparison with the prior art, overheat detection circuit in FIG. 4C, a constant-voltage source is introduced, and the base resistance is clamped to the output of the constant-voltage source.
In this semiconductor integrated circuit device, the leakage current from the well region to the base resistance is detected. The leakage current is stabilized by the constant-voltage source and is amplified by the transistor. And the operation of the bipolar transistor is stabilized because of the base resistance.
According to this invention, a semiconductor integrated circuit device, which detects an overheat based on the leakage current of the base resistance of the transistor, will be realized.
Another improvement is that in the above-mentioned device, the base resistance is located close to an elements and circuits protected from the overheat and located far from the constant-voltage source.
In this way the temperature of an object protected from overheat can be detected correctly based on the leakage current of the base resistance.
As the constant-voltage source which provide a certain voltage with the well region is located far from the protected objects, the constant-voltage source is not influenced by the thermal change caused by the overheat protected elements or circuits.
A certain voltage which contributes to a stabilization of the leakage current, is not influenced by the undesired thermal change. Therefore an overheat detection can be made correctly.
According to this second invention, a semiconductor integrated circuit device which can detect the overheat correctly based on the leakage current of the base resistance of the transistor.